Island



(No Model.)

H. A. HARVEY.

WOOD SCREW.

No. 362,833.- Patented May 10, 1887.

Nrrnn TATES HAYWARD A. HARVEY, OE ORANGE, NE\V JERSEY, ASSIGNOR TO THEAMERICAN SORE\V COMPANY, OF PROVIDENCE, RHODE ISLAND.

fwooo-scREw.

SPECIFICATION forming part of Letters Patent No. 362,833, dated May10,1887.

Application filed May 6, 1884. Serial No. 130,491. (No model.)

To all whom it may concern.-

Be it known that I, HAYWARD A. HARVEY, of Orange, New Jersey, haveinvented a certain Improvement in \Vood-Screws having Rolled Threads, ofwhich the following is a specification.

In the ordinary methods of rolling threads upon screw-blanks heretoforepracticed it is found that the shank of the screw-blank is likely to bebent by the action of the dies in forming the heel of the thread-thatis, in forming the convolution of the thread which commences nearest thehead of the blank. This occurs because at that point the blank is liableto be subjected to a greater pressure on one side than upon the other.

It is the object of the present invention to overcome this difficulty,and this object is accomplished by graduallydiminishingthe depth of thespiral groove formed upon the body of the blank as it approaches thehead of the blank. This gradual diminution of the depth of the spiralgroove gives to the part of the core adjoining the unthreaded portion ofthe body of the blank a conical form, and it also has the effect ofgradually lessening the extent to which the diameter of the thread isincreased by the act.of rolling the threads upon the blank. In this waythe part of the blank adjoining the unthreaded portion is not onlysubjected to less lateral strain by either of the dies,'but isstrengthened, so that it is better able to resist any lateral strain,and the result is the preservation of the threaded por tion of the bodyin perfect alignment with the unthreaded portion.

The progressive deepening of the spiral groove from the heel of thethread toward the point of the screw may, if desired, be continuedduring one or more convolutions of the thread, and will be variedaccording to the size of the screw and the ultimate depth of the thread.If a very deep thread is to be formed upon the blank, the progressivedeepening of the groove will be more gradual than when a shallowerthread is to be formed.

The accompanying drawings of a screw containing the invention are asfollows:

Figure 1 is an elevation, and Fig. 2 is a central longitudinal section.Fig. 3 is a transverse section of the screw, taken through the line X Xon Fig. 1.

It will be seen that the unthreaded portion a of the shank of the blankis of less diameter than the diameter of the threads, the effect ofrolling the threads being to cause a radially outward flow of the metalfrom the body of the blank. It will also be seen that the heelconvolution b of the thread-that is, the convolution next the head 0 ofthe screwgradually increases in diameter, so that its edge b has ahelical curve. It will also be seen that the portion (1 of the corewhich adjoins the unthreaded portion of the shank gradually diminishesin diameter. This diminution in the diameter of the core and increase inthe diameter of the thread continue until the thread has acquired itsfull depth upon the cylindrical portion 6 of the body Screws made in theordinary way-by having the threads formed by cutting a spiral groovearound the shank-have heretofore been made with cores similar to thecore of this improved screw, in respect of having the part of the coreadjoining the unthreaded portion of the shank conical; but in suchscrews the convolutions of the thread are of uniform diameter and are ofthe same diameter as the diameter of the unthreaded part of the blank.The improved screw herein described is distinguishable from such screwsby the peculiarity that the convolutions of the thread around theconical part of the core gradually increase in diameter from their pointof commencement near the head and acquire a larger diameter than thediameter of the unthreaded portion of the blank.

I claim as my invention- The improved screw herein described, whichconsists in a screw having a thread the convolutions of which graduallyincrease in diameter from their point of commencement adjoining theunthreaded part of the shank, while the part of the core adjoining theunthreaded portion of the shank gradually decreases in diameter untilthe thread has acquired its full depth.

H. A. HARVEY.

WVitnesses:

M. L. ADAMS, R. O. Howns.

